


A Heated Morning

by SoloShikigami



Category: Undertale (Video Game)
Genre: Alternate Universe, Brother/Brother Incest, Incest, M/M, Mating Cycles/In Heat
Language: English
Status: Completed
Published: 2020-04-22
Updated: 2020-04-22
Packaged: 2021-03-02 00:27:32
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,554
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23786314
Author URL: https://archiveofourown.org/users/SoloShikigami/pseuds/SoloShikigami
Summary: Sans has always been a bright, happy little skeleton, but one morning he's a little cranky, and Papyrus finds that he doesn't mind... especially when he figures out why.
Relationships: Papyrus/Sans (Undertale)
Comments: 2
Kudos: 78





	A Heated Morning

**Author's Note:**

> Written for MommyBrown1, originally posted in February of 2017!

Shy was the last word that Papyrus would ever use to describe his brother. From infancy, Sans had always been a bright and happy little skeleton. His enthusiasm tended to be a little much for most people, but it was what made Sans himself and Papyrus always loved him for it.

The only exception was when it came to intimacy, more notably, the sexual side of it.

Sans was free and easy with hugs, snuggles, little kisses, and other tokens of affection. Then when their relationship slowly pushed towards sex, Sans began to hold back.

Papyrus was shocked to find that Sans had quite the poor body image.

"Eh, mweh, Pappy, no," Sans murmured with a squirm when Papyrus had tried to lift his shirt with the intention of touching his rib cage.

"What's wrong, Sans?" Papyrus asked, backing away.

"I, uhm, just..." Sans looked away, his face flushed. "I... I'm not skinny like you, you know."

Papyrus blinked. "Well, yeah, you've always been big boned," he said, giving his brother a loving smile.

Sans squirmed uncomfortably. "Well, even when my magic, uhm, acts up, it still... I'm fat and gross."

"Oh, Sans, no, you’re not gross," Papyrus said gently, shuffling closer to Sans again. "Yes, you may have a bit extra on you, but you know, Alphys does, too."

"But it looks good on her!"

"Aww, Sans," Papyrus turned his face to kiss him. "I love you, I don't care what you look like."

Sans hummed into the kiss, gripping Papyrus' sweater. "Pappy," he murmured, still blushing and curling in on himself shyly.

"Please, let me see you, Sans, let me touch you."

Sans still seemed a bit reluctant, but he lay back and allowed Papyrus to gently touch him under his shirt, rubbing over the belly his magic would form when he was turned on, stroking over his bones, and Papyrus would spend a good deal of time showing Sans he loved his body just as much as the rest of him.

It was a pattern that would persist; Sans would start out enthusiastically, having no issues undressing his brother, pleasing him, but then when it was his turn, it took a little more convincing, but Papyrus didn't mind one bit.

One day, Sans woke up feeling off. He knew he wasn't sick, but he felt annoyed, irritated, and definitely _not_ like himself, which annoyed him even further.

He went down to the kitchen after dressing, though he kept tugging and readjusting his uniform; it was uncharacteristically uncomfortable that morning. He started making breakfast, grumbling to himself. Things just seemed to escalate; his finger got caught between two pans, he nearly burned his hand on the stove, and nearly cut himself with the knife.

“And why is it so hot in here?!” Sans growled, scowling as he waited for the meat to brown.

"Good morning, bro," Papyrus said, shuffling into the kitchen. He came up behind Sans and wrapped his arms around his shoulders, nuzzling the side of his skull. "How are you?"

Sans rolled his shoulders. "Don't touch me."

Papyrus blinked and let him go.

That was unusual.

"Are you all right?" Papyrus asked.

Sans slammed the spoon he was using to mix the taco meat. "No! I'm not!" He picked up the spoon again and angrily stirred the meat again. "Just leave me alone."

Papyrus frowned. "Did I do something wrong?"

"No! Just..." Sans took a deep breath to try to calm himself. "I just don't feel well."

"Then why are you cooking? I'll take care of you, just tell me what you need."

"I..." Sans dropped the spoon and stumbled back from the stove, putting one hand on his head.

"Sans!" Papyrus moved forward, his hands out to help Sans. He put one hand on his shoulder to steady him and reached with the other to turn off the stove.

Sans growled and turned and shoved Papyrus away.

"Just stop it!" Sans shouted.

Papyrus was so startled that he fell. He looked up at Sans, upset and worried, while Sans looked down at him.

The two just stared at each other. Papyrus watched Sans carefully, trying to figure out what was going on, while Sans mostly stared back blankly.

But inside of Sans, there was something much more chaotic going on. Heat flowed over his bones and agitated his magic. He was suddenly very aware of exactly where Papyrus was; if numbers made any sense to him he could tell down to the centimeter how far each part of Papyrus’ body was away from him. He could smell Papyrus; the tobacco from his cigarettes, the honey he probably overindulged in late last night, the laundry detergent, the scent that was just him and him alone – an earthy scent touched with something flowery - that would be left if everything else was stripped away.

“I, I’m so sorry, Papyrus,” Sans said softly, realizing that he had unintentionally hurt him. “I didn’t mean it.”

“It’s all right,” Papyrus said, smiling up at him. “Some days a monster just wakes up on the wrong side of the bed.”

Sans took a step forward, and then got onto his knees, and then crawled towards Papyrus. “No, I hurt you, I have to fix it.”

Sans moved closer, Papyrus spreading his legs a bit to let Sans settle between them. Sans pressed his hands to his chest, pushing him to lie flat on the floor and kissing him deeply.

“Mmm, not that I’m complaining, but really, Sans, I’m all right,” Papyrus said, stroking his brother’s skull.

“I’m going to fix it, Papyrus,” Sans breathed. “I want you.”

Papyrus stared. “Wha-?”

Sans sat up and yanked his shirt off before he shoved his hands under Papyrus’ sweater, pushing it up as he captured his mouth in another kiss, though this one was quite forceful. Papyrus was stunned into submission as Sans’ tongue pushed through, ravaging his mouth, distracted from Sans undoing his pants and shoving them down his legs. The kiss broke when Sans released him so he could finish taking the orange hoodie off. As soon as he was free of it, Sans kissed him again, his hands wandering over every part of him that he could touch.

“Sans, this, ahh, wha-what are you doing?” Papyrus asked, gasping as Sans’ mouth touched on sensitive spots along his clavicle.

“I love you, Papyrus, I love you so much,” Sans said, an edge of a possessive growl in his voice. “You’re mine, and I’m going to show you that you’re mine.”

Papyrus was still processing the proclamation when Sans suddenly bit down on his neck. The taller skeleton let out a hiss of pain, gripping Sans’ shoulder hard, but not feeling right pushing him away. Sans hummed as his tongue lapped over the shallow mark.

“Good boy, Papyrus,” Sans murmured.

Papyrus moaned; stars, when did his brother learn to sound like that?

“I’m going to take you, Papyrus,” Sans said, one hand reaching down to rub between Papyrus’ legs. “I’m going to prove to you how much I love you. Do you have any objections?”

Papyrus shook his head. “N-no, Sans, I, I want you, too, please, I’m yours.”

Sans chuckled. “Good.”

Papyrus whimpered a little as Sans kissed him again, his fingers moving through his own forming magic until he felt what he was looking for. Sans gripped his own formed cock, guiding it to Papyrus’ entrance and gently pushing inside.

“Oh, fuck, Sans,” Papyrus hissed, feeling his magic stretching around him.

“Language, brother,” Sans whispered, licking up his jaw as he pressed into him further.

Papyrus lost the ability to form words as Sans slowly moved in and out of him. Everything turned into a blur of movement, pleasure, panting as they chased their pleasures. Papyrus cried out and gripped Sans tightly as he came, Sans following soon after. The smaller skeleton collapsed on top of him with a small groan and Papyrus held him close.

“Sans, that, that was great,” Papyrus said. “Where did all of that come from?”

Sans only muttered a few incoherent sounds as he snuggled into his brother. Papyrus smiled, stroking the top of Sans’ skull.

Then it hit him.

“Sans?”

“Hmm?”

“Are you feeling hot?”

“Yeah, it’s uncomfortable.”

“Sans?”

“What is it, Papyrus?”

“You’re in heat.”

Sans finally moved to look up at Papyrus with bleary eyes. “What do you mean?”

“You’re going to be really, really horny for the next few days.”

Sans’ face flushed. “PAPYRUS!”

Papyrus rolled his eyes slightly as Sans buried his face into his ribcage again and shook his head.

“It’s okay, bro, we’ll get through this,” he reached down and hooked a finger under Sans’ chin to lift his face. “Together.”

Papyrus gave Sans a gentle kiss, who returned it eagerly.

“Well, I think we should clean up a bit and get something to eat. We’re going to need our energy. Oh, and you better call Alphys and let her know that you won’t be training for the next few days, if not the entire week.”

“Why is that?”

“Because we’re going to be too busy fucking each other into oblivion.”

“PAPYRUS! STOP IT!”

But as much as Sans sputtered and blushed, he knew that it was true, and he was thankful that his brother would be there to help him through it.

**Author's Note:**

> Like what you read? Please check out my social media for more fun!  
> [ My Tumblr](https://soloshikigami.tumblr.com/)  
> [ My Twitter](https://twitter.com/SoloShikigami)


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